<!DOCTYPE html>
<html>

<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        .login-header {
            width: 100%;
            text-align: center;
            height: 30px;
            font-size: 24px;
            line-height: 30px;
        }
        
        ul,
        li,
        ol,
        dl,
        dt,
        dd,
        div,
        p,
        span,
        h1,
        h2,
        h3,
        h4,
        h5,
        h6,
        a {
            padding: 0px;
            margin: 0px;
        }
        
        .login {
            display: none;
            width: 512px;
            height: 280px;
            position: fixed;
            border: #ebebeb solid 1px;
            left: 50%;
            top: 50%;
            background: #ffffff;
            box-shadow: 0px 0px 20px #ddd;
            z-index: 9999;
            transform: translate(-50%, -50%);
        }
        
        .login-title {
            width: 100%;
            margin: 10px 0px 0px 0px;
            text-align: center;
            line-height: 40px;
            height: 40px;
            font-size: 18px;
            position: relative;
            cursor: move;
        }
        
        .login-input-content {
            margin-top: 20px;
        }
        
        .login-button {
            width: 50%;
            margin: 30px auto 0px auto;
            line-height: 40px;
            font-size: 14px;
            border: #ebebeb 1px solid;
            text-align: center;
        }
        
        .login-bg {
            display: none;
            width: 100%;
            height: 100%;
            position: fixed;
            top: 0px;
            left: 0px;
            background: rgba(0, 0, 0, .3);
        }
        
        a {
            text-decoration: none;
            color: #000000;
        }
        
        .login-button a {
            display: block;
        }
        
        .login-input input.list-input {
            float: left;
            line-height: 35px;
            height: 35px;
            width: 350px;
            border: #ebebeb 1px solid;
            text-indent: 5px;
        }
        
        .login-input {
            overflow: hidden;
            margin: 0px 0px 20px 0px;
        }
        
        .login-input label {
            float: left;
            width: 90px;
            padding-right: 10px;
            text-align: right;
            line-height: 35px;
            height: 35px;
            font-size: 14px;
        }
        
        .login-title span {
            position: absolute;
            font-size: 12px;
            right: -20px;
            top: -30px;
            background: #ffffff;
            border: #ebebeb solid 1px;
            width: 40px;
            height: 40px;
            border-radius: 20px;
        }
    </style>
</head>

<body>
    <div class="login-header"><a id="link" href="javascript:;">点击，弹出登录框</a></div>
    <div id="login" class="login">
        <div id="title" class="login-title">登录会员
            <span><a id="closeBtn" href="javascript:void(0);" class="close-login">关闭</a></span>
        </div>
        <div class="login-input-content">
            <div class="login-input">
                <label>用户名：</label>
                <input type="text" placeholder="请输入用户名" name="info[username]" id="username" class="list-input">
            </div>
            <div class="login-input">
                <label>登录密码：</label>
                <input type="password" placeholder="请输入登录密码" name="info[password]" id="password" class="list-input">
            </div>
        </div>
        <div id="loginBtn" class="login-button"><a href="javascript:void(0);" id="login-button-submit">登录会员</a></div>
    </div>
    <!-- 遮盖层 -->
    <div id="bg" class="login-bg"></div>
    <script src="http://libs.baidu.com/jquery/2.0.0/jquery.min.js"></script>
    <script>
        // 1. 获取元素
        var login = document.querySelector('.login');
        var mask = document.querySelector('.login-bg');
        var link = document.querySelector('#link');
        var closeBtn = document.querySelector('#closeBtn');
        var title = document.querySelector('#title');

        link.onclick = function() {
                login.style.display = 'block';
                mask.style.display = 'block';
            }
            // 获取到要拖拽的元素
        drag(login); // 调用自己封装的拖拽函数

        function drag(obj) {
            obj.onmousedown = function(e) {

                var e = e || window.event; // 兼容 IE
                // 鼠标点击物体那一刻相对于物体左侧边框的距离=点击时的位置相对于浏览器
                // 最左边的距离-物体左边框相对于浏览器最左边的距离，纵向同理
                var divX = e.clientX - this.offsetLeft;
                var divY = e.clientY - this.offsetTop;

                if (obj.setCapture) {
                    obj.setCapture(); // 修复低版本 IE bug
                }

                document.onmousemove = function(e) {

                    var e = e || window.event;

                    var disX = e.clientX - divX;
                    var disY = e.clientY - divY;

                    // 控制拖拽物体的范围只能在浏览器视窗内，不允许出现滚动条或拖出可视区域
                    if (disX < 0) {
                        disX = 0;
                    } else if (disX > document.documentElement.clientWidth - obj.offsetWidth) {
                        disX = document.documentElement.clientWidth - obj.offsetWidth;
                    }

                    if (disY < 0) {
                        disY = 0;
                    } else if (disY > document.documentElement.clientHeight - obj.offsetHeight) {
                        disY = document.documentElement.clientHeight - obj.offsetHeight;
                    }

                    // 移动时重新得到物体的距离，解决拖动时出现晃动现象  
                    obj.style.top = disY + "px";
                    obj.style.left = disX + "px";

                    document.onmouseup = function() { // 鼠标抬起时不再移动  
                        // 预防鼠标弹起来后还会循环（即预防鼠标放上去的时候还会移动）
                        document.onmousedown = document.onmousemove = null;
                        if (obj.releaseCapture) {
                            obj.releaseCapture(); // 修复低版本 IE bug
                        }
                    }
                }
            }
        }
        closeBtn.onclick = function() {
            login.style.display = 'none';
            mask.style.display = 'block';
        }
    </script>
</body>

</html>